I always knew I was adopted. My mother told me I'd been chosen and I should feel extra special. A tall blonde growing up with short, brunette Jewish parents, all I ever felt was awkward and out of place.

When I was about nine, I began to think endlessly about my biological parents. Was my father athletic, like me? Did I have my mother's blue eyes? I stared at people on the street, fantasising that they were my birth parents.

I was 12 when I told my adoptive parents I wanted to find my birth mother. I was being bullied at school, because I looked so different from the other girls, and felt lost and unhappy. I thought if I could find out where I came from, I would somehow fit in better.

They were supportive, and gave me the name of the adoption lawyer they'd used, but he told me I had to be 18. I called him back on the day of my 18th birthday. I discovered my mother was Caucasian, with German, Irish and English ancestry, and had been 31 when she had me. I had a brother and a sister who were 11 and 13 when I was born. Under "Father" it simply stated: "Caucasian, of large build."

I was confused. My father had obviously not been her husband, as I'd assumed. I read the file over and over, analysing every word. "It sounds like a police description," I said to my adoptive mum. Then an awful thought struck me. Had my mother been raped? The more I studied the file, the more convinced I became. I rang my case worker.

"Was my mum raped?" I asked straight out, catching her off guard.

"Yes," she replied. The confirmation was devastating. No wonder my mother had given me up; I was an unbearable reminder of a violent attack. My adoptive parents tried to reassure me I was loved, but my confidence was destroyed.

I remembered reading a psychology book that said deviant behaviour was genetic. I worried that evil was embedded in my genes, and that people could tell, somehow, that I'd been created from violence. If I went on to have a son, would he be a rapist, too?

A tiny part of me clung to the hope that the file was wrong; that my birth mother had lied about the rape, because she'd had an affair. I had to know for sure, so I wrote to the courts asking if they'd contact her on my behalf. A few weeks later I heard back; she wanted to speak to me.

I was forwarded my full adoption file, and discovered my birth name had been Judy Ann Miracle. My birth mother had since remarried, but the file also included her married name, address and telephone number. She lived just 20 minutes' drive from me.

Shaking with nerves, I rang the number, and she picked up. "I've been expecting your call," she told me. She said she'd never forgotten me, and had celebrated my birthday every year.

"I'm sorry you already know about the rape," she said, and a great sadness flooded through me; so it was true, and worse than I'd imagined. She'd been on her way to the grocery store when a man appeared in front of her, smelling of alcohol. He pulled out a knife, forced her to a nearby field and raped her. Although he was never arrested, police were sure her attacker was a serial rapist who was later jailed for murder.

When she discovered she was pregnant, she went to see a rape counsellor, who advised her to terminate the pregnancy. She booked in at two illegal clinics, but cancelled both times because she was worried about her safety. Had abortion been legal in Michigan in 1969, she admitted, she'd have gone through with it.

We spoke for two hours. At the end of the call she told me she'd always loved me. "You were perfect," she reassured me.

When I met up with her a few months later, she showed me the spot where she'd been abducted. She was so matter-of-fact – she'd had 20 years to come to terms with the attack – but it was still fresh for me, and I found it terribly upsetting.

When I was 27, I met my husband Bob and, slowly, he helped me to understand that my father's crimes had nothing to do with me. Having children of my own has also helped. I realise now that being conceived by rape doesn't define me. It's not just genes that make a person, it's how you choose to live your life.